PRODUCT DATA
Free-field ¼-inch Microphone — Type 4939
The Free-field ¼″ Microphone is specially designed for high level and high frequency measurements. By
using stainless steel diaphragm and protection grid, the microphone is optimised to withstand rough
environments and is capable of working at high temperatures – up to 150°C (302°F).
USES
❍ High level measurements
❍ High frequency measurements
❍ Model work
FEATURES
❍ Sensitivity:
4 mV/Pa
❍ Frequency:
4 – 100,000 Hz
❍ Dynamic Range: 28 – 164 dB
❍ Temperature:
–40 to 150°C
(–40 to 302°F)
❍ Polarization:
200 V External
Robustness
The microphone is capable of withstanding the IEC 68-2-32 1 metre drop test.
Assembly
The assembly of the microphone in a clean room environment ensures that the microphone can be used in high humidity environments and still produce reliable results.
Microphone Data Disk
The microphone is supplied with a 3 ½″ microphone data disk. This disk includes all
calibration data as well as free-field, random-incidence and pressure-field corrections.
The influence of the ¼″ Nose Cone is also available.
Calibration
The sensitivity can be calibrated at 250 Hz by using Pistonphone Type 4228 with ¼″
Adaptor DP 0775. The actuator response can be measured using Actuator UA 0033 with
Adaptor DB 0264. The free-field response can be obtained by adding the type-specific,
free-field correction to the actuator response.
More Information
Further information on stability, effect of environmental influence, directional characteristics and detailed specifications can be found in The Microphone Handbook
(BA 5105).
Fig. 1 Type 4939
free-field response
without grid
Response (dB)
5
0
-5
-10
1
10
100
1000
Frequency (Hz)
10000
100000
1000000
990046e
Specifications – Free-field ¼-inch Microphone Type 4939
Typical Uses: General high level, high frequency measurements
and model work
Nominal Diameter: ¼″
Open Circuit Sensitivity (250 Hz)*: –48 ±3 dB re 1 V/Pa, 4 mV/Pa
Polarization Voltage: 200 V external
Frequency Response*:
Free-field Response 4 Hz to 100 kHz: ±2 dB. In accordance with
IEC 61094 – 4 WS3F
Lower Limiting Frequency (–3 dB): 0.3 Hz to 3 Hz
Pressure Equalization Vent: Side vented
Diaphragm Resonance Frequency: 80 kHz (90° phase-shift)
Capacitance (Polarized 250 Hz)*: 6.1 pF at 250 Hz
Equivalent Air Volume: 0.6 mm3 (250 Hz)
Cartridge Thermal Noise: 28 dB(A) 33 dB (Lin, 20 – 100 kHz)
Upper Limit of Dynamic Range (3% Distortion): >164 dB SPL
Maximum Sound Pressure Level: 174 dB (peak)
Environmental
Operating Temperature Range: –40 to 150°C (–40 to 302°F)
Storage Temperature:
In case: –30 to +70°C (–22 to 158°F)
With data disk: 5 to 50°C (41 to 122°F)
*Individually
Temperature Coefficient (250 Hz): +0.003 dB/°C (–10 to 50°C,
14 to 122°F)
Pressure Coefficient: –0.007 dB/kPa, typical
Operating Humidity Range: 0 to 100%RH (without condensation)
Influence of Humidity: <0.1 dB in the absence of condensation
Vibration Sensitivity (<1000 Hz): 60 dB equivalent SPL for 1m/s2
axial vibration
Magnetic Field Sensitivity: 10 dB SPL for 80 A/m, 50 Hz field
Dimensions
Diameter with Grid: 7 mm (0.27 in)
Diameter without Grid: 6.35 mm (0.25 in)
Height with Grid: 10.5 mm (0.41 in)
Height without Grid: 9 mm (0.35 in)
Thread for Preamplifier Mounting: 5.7 mm – 60UNS
Note: All values are typical at 23°C (73.4°F), 101.3 kPa and 50%
RH, unless measurement uncertainty or tolerance field is
specified. All uncertainty values are specified at 2σ (i.e.,
expanded uncertainty using a coverage factor of 2)
compliance with EMC Directive
calibrated
†Quote
microphone serial number if re-ordering
Optional Accessories
Type 2670
DP 0775
DB 0264
UA 0033
UA 0385
BA 5105
¼″ Microphone Preamplifier
Calibration Adaptor for ¼″ microphones
½″ to ¼″ Adaptor for UA 0033
Electrostatic Actuator
Nose Cone for ¼″ microphones
The Microphone Handbook
Brüel & Kjær reserves the right to change specifications and accessories without notice.
HEADQUARTERS: DK-2850 Nærum · Denmark · Telephone: +4545800500 · Fax: +4545801405 · http://www.bk.dk · e-mail: info@bk.dk
Australia (02)9450-2066 · Austria 0043-1-8657400 · Brazil (011)5182-8166 · Canada (514)695-8225 · China 1068029906
Czech Republic 02-67021100 · Finland (0)9-755 950 · France (01)69906900 · Germany 06103/908-5 6 · Hong Kong 25487486 · Hungary (1)2158305
Ireland (01) 450 4922 · Italy (02)57604141 · Japan 03-3779-8671 · Republic of Korea (02)3473-0605 · Netherlands (0)30 6039994 · Norway 66771155
Poland (0-22)8409392 · Portugal (1)4711453 · Singapore (65) 275-8816 · Slovak Republic 421 7 544 307 01 · Spain (91)3681000 · Sweden (08)4498600
Switzerland 01/9436070 · Taiwan (02)7139303 · United Kingdom (0181)954-2366 · USA 18003322040
Local representatives and service organisations worldwide
BP 1851 – 11
Type 4939
Free-field ¼″ Microphone
Includes the following accessories:
BC 0229
Calibration Chart †
BC 5002
Microphone Data Disk†
99/04
Ordering Information